There's no telling how long it will take for Google to index your backlinks. Most people find it takes several weeks, but it varies greatly. Any services which promises 24 indexing cannot possibly deliver. Nevertheless, there are things you can do to help your backlinks get indexed more quickly unless a site will not allow it using their robots.txt file. In this case, you are out of luck.
Backlinks from older, authoritative domains usually enjoy backlink indexation quickly. Google also generally indexes backlinks from news websites, which publish fresh content daily, more rapidly. Backlinks from blog comments are other low-quality sources take longer for Google to index, if they bother at all.
Pinging your backlinks does not work anymore. It is awful to feel you've wasted your time building backlinks when they don't get indexed. If you find a free pinging tool, like Ping-O-Matic or Ping My Links, you can manually pink sites one at a time; it can't hurt. Keep a record to see if any of your previously nonindexed backlinks are indexed.
Tier two link building can help your primary link get indexed faster. Second-tier links showcase the content around the first-tier link. You can use social media to link to the content containing your backlink; this is second-tier linking.
Although it is a bad practice, if you buy links from somewhere, such as Fivver, Google may never index them. Sometimes, the links are on sites which don't have Google indexation because they are too new or because of a ban for bad SEO practices. Either way, if the website providing the backlink isn't in Google's index, your backlink won't be there either.
Build a backlink profile the right way, either earning them naturally with superior content or by writing guest posts for authoritative websites. This way. you'll have a good chance of getting backlinks which Google will index. For more information click here https://www.reddit.com/r/SEO/comments/c4krou/backlinks_indexing/.